Base substrate, functional element, and production method for base substrate

ABSTRACT

A base substrate includes a supporting substrate and a base crystal layer provided on a main face of the supporting substrate composed of a crystal of a group 13 nitride and having a crystal growth surface. The base crystal layer includes a raised part. A reaction product of a material of the supporting substrate and the crystal of the group 13 nitride, metal of a group 13 element and/or void is present between the raised part and supporting substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT/JP2018/025154, filed Jul. 3, 2018, whichclaims priority to Japanese Application No. 2017-186340, filed Sep. 27,2017, the entire contents of which are hereby incorporated by reference.

BACKGROUND ARTS

Light-emitting devices such as light emitting diodes (LEDs) that usesapphire (α-alumina single crystal) as a monocrystalline substrate, withvarious types of gallium nitride (GaN) layers formed thereon are known.For example, light-emitting devices have been mass-produced having astructure in which an n-type GaN layer, a multiple quantum well (MQW)layer with an InGaN quantum well layer and a GaN barrier layer laminatedalternately therein and a p-type GaN layer are formed in a laminatedmanner in this order on a sapphire substrate.

It has been proposed, in a base substrate (template substrate) forgrowing a layer of a crystal of a group 13 nitride such as galliumnitride, to provide an irregularity on a crystal growth surface of abase crystal layer of the base substrate. That is, according to patentdocuments 1 to 3, it has been disclosed the procedure of forming theirregularity on the crystal growth surface of the base substrate toreduce dislocations and stress in a crystal.

According to patent document 2, the growth surface of the base crystallayer is made a flat c-plane and an inclined surface inclined withrespect to a c-plane and without including a plane parallel with thec-plane is made continuous to form the irregularity.

According to patent document 3, on the crystal growth surface of thebase substrate, a flat part of +c-plane and a flat and inclined surfaceto which non-+c-plane is exposed is formed. According to patent document3, rectangular projections and recesses are formed on the crystal growthsurface of the base substrate.

Further, according to patent document 4, in the case that a seed crystalfilm is formed on a sapphire substrate, it is proposed that voids areformed along an interface of the sapphire substrate by heating or alaser and seed crystal film and that the void ratio is made 12.5% orlower. Cracks or fractures of a gallium nitride crystal layer arethereby suppressed.

PATENT DOCUMENTS

(Patent document 1) Japanese Patent No. 5359740B

(Patent document 2) Japanese Patent Publication No. 2017-036174A

(Patent document 3) Japanese Patent Publication No. 2005-281067A

(Patent document 4) Japanese Patent No. 6144630B

SUMMARY OF THE INVENTION

Although a crystal of a group 13 nitride is easily associated in thedirection of an a-axis, the association in the direction of a m-axis isdifficult. Thus, according to the base substrates of patent documents 1to 3, when the crystal of the group 13 nitride is grown into a thinfilm, the disassociation of the crystals may occur or the sufficientreduction of pits may be difficult so that the reduction of thedislocation density is limited in regions where the crystal is grown inthe direction of an axis other than the c-axis and a-axis. Thus, when anLED is produced on the disassociation parts or pits of the substrate, itis proved that a leak may occur to reduce the production yield.

An object of the present invention is, in a base substrate for growing acrystal of a group 13 nitride on a crystal growth surface of a basecrystal layer, to provide a structure capable of further reducing adislocation density of the layer of the crystal of the group 13 nitride.

The present invention provides a base substrate comprising:

a supporting substrate; and

a base crystal layer provided on a main face of the supportingsubstrate, comprising a crystal of a nitride of a group 13 element andhaving a crystal growth surface,

wherein the base crystal layer comprises a raised part; and

wherein a reaction product of a material of the supporting substrate andthe crystal of the nitride of the group 13 element, a metal of a group13 element and/or a void is present between the raised part and thesupporting substrate.

The present invention further provides a base substrate comprising:

a supporting substrate; and

a base crystal layer provided on a main face of the supportingsubstrate, comprising a crystal of a nitride of a group 13 element andhaving a crystal growth surface,

wherein the base crystal layer comprises a raised part;

wherein the crystal growth surface forms a curved line; and

wherein a height of the crystal growth surface on the curved line withrespect to the main face is smoothly changed, provided that the raisedpart is viewed along a cross section perpendicular to the main face ofthe supporting substrate.

The present invention further provides a functional device comprising:

the base substrate; and

a functional layer provided on the base crystal layer.

According to the present invention, the structure that the base crystallayer includes the raised part and that the reaction product of thematerial of the supporting substrate and crystal of the nitride of thegroup 13 element, the metal of the group 13 element and/or the void ispresent between the raised part and the supporting substrate isprovided. According to this structure, the association of the layer ofthe crystal of the group 13 nitride is facilitated over the crystalgrowth surface, so that pits generated by the disassociation are reducedand the dislocation density of the layer of the crystal of the group 13nitride is reduced.

Further, the structure is provided that the raised part is provided inthe base crystal layer, that the crystal growth surface forms a curvedline and that a height of the crystal growth surface on the curved linewith respect to the main face is smoothly changed, provided that theraised part is viewed along the cross section perpendicular to the mainface of the supporting substrate. According to this structure, theassociation of the layer of the crystal of the group 13 nitride isfacilitated over the crystal growth surface, so that pits generated bythe disassociation are reduced and the dislocation density of the layerof the crystal of the group 13 nitride is reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) shows the state that a base crystal layer 2 is provided on asupporting substrate 1, and FIG. 1(b) shows the state that a raised part5 is provided on a base crystal layer 3.

FIG. 2(a) shows the state that a thin layer 7 of a crystal of a group 13nitride is provided on the base crystal layer 3, and FIG. 2(b) show thestate that a thick film of a layer 8 of a crystal of a group 13 nitrideis provided on the base crystal layer 3.

FIGS. 3(a), 3(b) and 3(c) show the state that raised parts 5, 5A and 5Bare provided on the base crystal layer 3, respectively.

FIGS. 4(a), 4(b) and 4(c) show the state that raised parts 5C, 5D and 5Eare provided on the base crystal layer 3, respectively.

FIG. 5(a) shows the state that the raised part 5C is provided on thebase crystal layer 3, FIG. 5(b) show the state that the raised part 5and a flat part 3 d are provided on the base crystal layer 3, and FIG.5(c) shows the state that a plurality of raised parts 5 continuous witheach other are provided on the base crystal layer 3.

FIGS. 6(a) and 6(b) show planar patterns of base crystal layers 3,respectively.

FIGS. 7(a) and 7(b) show planar patterns of raised parts of base crystallayers 3, respectively.

FIGS. 8(a) and 8(b) show planar patterns of raised parts of base crystallayers 3, respectively.

FIGS. 9(a) and 9(b) show planar patterns of raised parts of base crystallayers 3, respectively.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The present invention will be described further in detail, appropriatelyreferring to the drawings.

As shown in FIG. 1(a), a base crystal layer 2 is film-formed on a mainface 1 a of a supporting substrate 1. 1 b represents a bottom face ofthe supporting substrate 1. Laser light is then irradiated as arrows Afrom the side of the bottom surface 1 b of the supporting substrate 1.The laser light passes through the supporting substrate 1 and reaches aninterface between the base crystal layer 2 and supporting substrate 1.

Here, the energy of the laser light is adjusted so that a reactionproduct 4 of materials of the supporting substrate and base crystallayer is generated between the supporting substrate and base crystallayer, as shown in FIG. 1(b). According to the present example, thereaction product 4 contacts the main face 1 a of the supportingsubstrate 1 and an interface 3 b of the base crystal layer 3. As aresult, a curved part 3 c of the base crystal layer 3 is curved andraised on the upper side of the raised part 4. On the other hand, thebase crystal layer 3 contacts the main face 1 a of the supportingsubstrate at locations where the reaction product 4 is not generated. 3a represents a crystal growth surface and 6 represents a base substrate.

Further, a metal of a group 13 element may be generated instead of thereaction product, or both the reaction product and the metal of thegroup 13 element may be generated.

Then, as shown in FIG. 2(a), a crystal (thin film) 7 of a nitride of agroup 13 element may be grown on the crystal growth surface 3 a of thebase crystal layer 3. 20 represent a growth surface of a functionaldevice.

Alternatively, as shown in FIG. 2 b), a crystal 8 (thin film) of acrystal of a group 13 nitride may be grown on the growth surface 3 a ofthe base crystal layer 3. 20 represent the growth surface of thefunctional device. At this stage, the crystal 8 of the group 13 nitridemay be used as a template substrate without separating it from thesupporting substrate 1. However, the crystal 8 of the group 13 nitridemay be separated from the supporting substrate to provide aself-standing substrate, which may be used as a template substrate.

A functional device structure is then formed on the crystal 7 or 8 ofthe group 13 nitride. Although the kind of the functional devicestructure is not particularly limited, a light-emitting device may belisted. Further, a plurality of the functional layers may be formed onthe crystal.

Preferably, as shown in FIG. 1(b), the curved part 3 c of the crystalgrowth surface 3 forms a curved line, and the height h of the crystalgrowth surface 1 a on the curved line with respect to the main face 1 ais smoothly changed, provided that the raised part is viewed along across section (cross section shown in FIG. 1(b)) perpendicular to themain face 1 a of the supporting substrate. The height h is a height withrespect to the main face of the supporting substrate in a direction thenormal line P. According to this structure, the association of the layerof the crystal of the group 13 nitride is facilitated on the crystalgrowth surface, so that pits generated by the disassociation are reducedand the dislocation density of the layer of the crystal of the group 13nitride is reduced when the layer 7 or 8 of the crystal of the group 13nitride is film-formed on the crystal growth surface.

Constituents of the present invention will be further described below.

According to the inventive production method, a base crystal layercomposed of a group 13 nitride is provided on a supporting substrate.

Here, as a material forming the supporting substrate, a material isselected having a bandgap larger than a bandgap of the group 13 nitrideformed on the base crystal layer. When the material of the group 13nitride formed on the base crystal layer is gallium nitride, as itsbandgap is about 3.4 eV, the material of the supporting substrateincludes sapphire, crystalline orientated aluminum, gallium oxide, andAlxGa1-xN (0<x≤1). Preferably, the material of the supporting substratehas a composition of Al₂O₃.

The bottom face of the supporting substrate opposite to the base crystallayer may be a mirror surface or a roughened surface and preferably bethe roughened surface. By this, after the laser light incident into thesupporting substrate is scattered at the bottom surface of thesupporting substrate, the laser light is irradiated onto the basecrystal layer at the interface, so that the effects of the beam profileof the laser light is suppressed. When the bottom face of the supportingsubstrate opposite to the base crystal layer is the roughened surface,the arithmetic surface roughness Ra of the roughened surface maypreferably be 0.1 to 2 μm.

When the bottom face of the supporting substrate is the mirror face, itis easy to form the raised part pattern using spots of the laser light.Alternatively, a protective layer, which does not transmit the laserlight, may be formed on the bottom face of the supporting substrate andthen patterned to control the pattern of the raised part on the surface.

From the viewpoint of preventing cracks in the supporting substratedirectly after the cooling, the thickness of the supporting substratemay preferably be 0.5 mm or larger and more preferably be 1 mm orlarger. Further, from the viewpoint of handling, the thickness of thesupporting substrate may preferably be 3 mm or smaller.

A base crystal layer composed of a group 13 nitride is then provided onthe supporting substrate.

When the base crystal layer is formed, preferably, a buffer layer isprovided on the supporting substrate and the base crystal layer is thengrown thereon.

The method of forming this buffer layer may preferably be a vapor phaseprocesses including metal organic chemical vapor deposition (MOCVD),hydride vapor epitaxy (HVPE), molecular beam epitaxy (MBE) andsublimation.

The base crystal layer may be a single layer or may include the bufferlayer on the side of the supporting substrate. The method of forming thebase crystal layer may be vapor phase processes as one preferredexample, including metal organic chemical vapor deposition (MOCVD),hydride vapor epitaxy (HVPE), pulsed excitation deposition (PXD),molecular beam epitaxy (MBE) and sublimation. Metal organic chemicalvapor deposition is particularly preferred.

Further, in the group 13 nitride forming the base crystal layer, thegroup 13 element means a group 13 element in the Periodic Table definedby IUPAC. The group 13 element is specifically gallium, aluminum,indium, thallium or the like.

From the viewpoint of preventing melt-back or disappearance during thecrystal growth, the thickness of the base crystal layer may preferablybe 0.5 μm or larger and more preferably be 2 μm or larger. Further, fromthe viewpoint of productivity, the thickness of the base crystal layermay preferably be 15 μm or smaller.

Then, the laser light is irradiated from the side of the supportingsubstrate, the reaction product of the material of the supportingsubstrate and crystal of the group 13 nitride, metal of the group 13element and/or void is generated between the base crystal layer andsupporting substrate, so that the base crystal layer is raised. It isthereby possible to provide the raised part above the reaction product,metal of the group 13 element and/or void.

In this case, by the laser irradiation, the layer of the crystal of thegroup 13 nitride AN (A represents one or more element (s) selected fromthe group 13 elements such as Ga, In, Ta, Al or the like) is decomposedinto A and N, and A is then diffused into the supporting substrate togenerate the reaction product 4. The reaction product 4 has acomposition containing at least A and an element forming the supportingsubstrate. Then, the reaction product may be an alloy of A and theelement forming the supporting substrate, or a composition of theelement forming the supporting substrate and oxygen. The element formingthe supporting substrate may preferably be aluminum.

According to a preferred embodiment, the composition of the reactionproduct is as follows as a whole of the reaction product.

A (A represents a single group 13 element other than Al, or a pluralityof group 13 elements including Al):0.1 to 99.5 mol % (preferably 0.1 to40 mol %, particularly preferably 0.5 to 40 mol %)

Al: 0.5 to 99 mol % (preferably 29 to 54 mol %, particularly preferably29 to 50.5 mol %)

O: 0 to 50 mol % (Preferably 31 to 50 mol %, particularly preferably 31to 49 mol %)

When the supporting substrate is aluminum oxide and A is Al, thecomposition of the reaction product is as follows as a whole of thereaction product.

Al: 50 to 100 mol % (Preferably 50 to 72 mol %, particularly preferably51 to 69 mol %)

O: 0 to 50 mol % (Preferably 28 to 50 mol %, particularly preferably 31to 49 mol %)

However, it is not necessary that reaction product as a whole have auniform composition distribution, and the composition of the reactionproduct may have inclined compositions. For example, on the side of thesupporting substrate of the reaction product, the molar ratios ofaluminum and oxygen may be relatively higher and the molar ratio of thegroup 13 element may be relatively lower. On the other hand, on the sideof the base crystal layer of the reaction product, the molar ratios ofaluminum and oxygen may be relatively lower and the molar ratio of thegroup 13 element may be relatively higher.

Further, according to an embodiment, the reaction product A, reactionproduct B or the metal of the group 13 element A (A represents a group13 element other than Al) may be generated on the side of the crystal ofthe group 13 element.

(Reaction Product A)

A: 87 to 97.5 mol %

Al: 0.5 to 3 mol %

O: 2 to 10 mol %

(Reaction Product B)

A: 95 to 99.5 mol %

Al: 0.5 to 5 mol %

Further, according to an embodiment, first, second and third layers aregenerated from the layer of the crystal of the group 13 element to thesupporting substrate as follows.

First layer: Reaction product A, reaction product B or metal of a group13 element A (A represents a group 13 element other than Al)

Second Layer:

A: 0.5 to 40 mol %

Al: 29 to 50.5 mol %

O: 31 to 49 mol %

Third Layer:

A: 0.1 to 0.4 mol %

Al: 50 to 54 mol %

O: 45 to 50 mol %

Then, the method of analyzing the compositions of the reaction productsis as follows.

Measurement System:

A element analyzing system (“JED-2300T” supplied by JEOL Ltd.) is usedto perform the elemental analysis.

Measurement Conditions:

A sample is thinned by a FIB (focused ion beam) method and subjected toanalysis at an acceleration voltage or 200 kV, an X-ray extraction angleof 21.9°, a solid angle of 0.98 s r and a capture time of 30 seconds.

The thickness of the reaction product or metal of the group 13 elementis not particularly limited. From the viewpoint of suppressing thewarping or cracking of the layer of the crystal of the group 13 nitride,the thickness of the reaction product or metal of the group 13 elementmay preferably be 1 nm or larger. Further, from the viewpoint ofgenerating the raised part, the thickness of the reaction product ormetal of the group 13 element may preferably be 10 nm or larger and morepreferably be 100 nm or larger. Further, from the viewpoint of reducingthe dislocation density of the layer of the crystal of the group 13nitride, the thickness of the reaction product or metal of the group 13element may preferably be 500 nm or smaller and more preferably be 400nm or smaller.

Here, the energy of the laser light irradiated from the side of thesupporting substrate is adjusted so that the reaction product or metalof the group 13 element can be generated on the main face of thesupporting substrate. And the reaction product and metal of the group 13element can be generated under the raised part at the same time or onlythe void can be generated under the raised part.

For example, according to an example of FIG. 3(a), the reaction product4 is generated under the raised part 5 and the base crystal layer israised by the reaction product 4. On the other hand, according to anexample of FIG. 3(b), a void 9 is generated between the supportingsubstrate 1 and base crystal layer 3 and the base crystal layer 3 israised by the void 9 to form a raised part 5A.

Further, according to an example of FIG. 3(c), the void 9 and reactionproduct 4 are generated between the supporting substrate 1 and basecrystal layer 3 and the base crystal layer 3 is raised by the void 9 andreaction product 4 to form a raised part 5B. Further, according to anexample of FIG. 4(a), the void 9 is generated between the supportingsubstrate 1 and base crystal layer 3 and the base crystal layer 3 israised by the void 9 to form a raised part 5C. According to the presentexample, the void 9 is present over the reaction product 4.

Further, the void may provide cracks inside of the base crystal layer 3and the void may reach the surface of the raised part of the basecrystal layer 3 to form a recess. For example, according to an exampleof FIG. 4(b), the elongate void 9 is extended inside of a raised part 5Dto form a kind of a crack. Further, according to an example of FIG.4(c), the void 9 is generated under the raised part 5E and the tip endof the void 9 reaches to the surface of the raised part 5E to form arecess.

Further, according to an example of FIG. 5(a), the void 9 and reactionproduct 4 are generated between the supporting substrate 1 and basecrystal layer 3 and the base crystal layer 3 is raised by the void 9 andreaction product 4 to form a raised part 5C. However, the reactionproduct 4 is positioned in an inside half of the raised part and thevoid 9 is positioned in a half on the opposite side of the reactionproduct in the raised part.

For example, as illustrated referring to FIG. 1(b), the curved part ofthe crystal growth surface 3 forms a curved line and a height h of thecrystal growth surface 3 a on the curved line with respect to the mainface 1 a is smoothly changed, provided that the raised part 5 is viewedalong a cross section perpendicular to the main face 1 a of thesupporting substrate 1. As the height h of the curved part 3 c of thecrystal growth surface 3 on the raised part surface is differentiated toobtain an inclined angle of the crystal growth surface 3 a. Thus, theheight of the crystal growth surface 3 is smoothly changed, indicatingthat the inclined angle of the crystal growth surface 3 a iscontinuously changed without a cornered part at which the inclined angleis discontinuously changed. It is, however, permitted that a recess orcrack is present locally.

Then, although the cross-sectional shape of the profile of the crystalgrowth surface of the raised part is not specifically limited, variousshapes such as a circle arc, ellipse arc, hyperbola, parabola, racetrack or the like may be listed.

The dimension of each raised part is not particularly limited. However,from the viewpoint of reducing the dislocation density of the layer ofthe crystal of the group 13 nitride, the area of the raised part viewedin a plan view may preferably be 1 μm² to 0.8 mm². Further, the maximumvalue of the height h of the raised part with respect to the main facemay preferably be 10 to 1000 nm and more preferably be 100 to 700 nm,from the viewpoint of the productivity.

Further, the ratio of the area of the raised part in the whole area ofthe crystal growth surface of the base crystal layer may preferably be 5to 80% from the viewpoint of the present invention and, more preferably,be 15 to 60% from the viewpoint of productivity.

The dimension of the raised part was measured using ZYGO(Three-dimensional optical profiler “New View 7300” supplied by Canoncorporation) at the measurement condition of 5-fold in a visual field of1.4 mm and 1 mm to measure the heights of the raised parts to beobserved and the arithmetic average of the heights is taken as anaverage height of the raised parts. Further, the ratio of the raisedpart is calculated by performing binary processing using an imageanalysis software “WinROOF” (supplied by MITANI CORPORATION).

Further, as shown in FIG. 5(b), a flat part 3 d may be provided betweenthe raised parts 5. Alternatively, as shown in FIG. 5(c), the adjacentraised parts 5 may be made continuous without intervening the flat part.In this case, a recess 10 is generated between the adjacent raised parts5.

The planar shape of the raised part is not particularly limited. Forexample, according to an example of FIG. 6(a), many island-shaped raisedparts 5 are formed on the crystal growth surface 3 a and the flat parts3 d are provided between the adjacent raised parts 5. Each of the raisedparts forms a separate phase and the flat parts 3 d form a network-likecontinuous phase.

According an example of FIG. 6(b), raised parts 5E are patterned intostripe-shaped pattern. However, as the raised part 5E is enlarged, manyraised parts may be made continuous as shown in FIG. 5(b). Thus, theedge 11 of the raised part 5E may form an irregular curved line and maynot be straight line-shaped.

In the case of the patterning of the raised parts as a whole, thepattern of the raised parts is not particularly limited. According tothe examples shown in FIGS. 7(a) and 7(b), many stripe-shaped raisedparts 5E are arranged in lines. Further, according to an example of FIG.8(a), network and lattice forming raised parts 5F are formed and,according to an example of FIG. 8(b), raised parts 5 are formed as dotsor scattered points or islands.

Further, according to the examples of FIGS. 9(a) and 9(b), raised parts5G and 5H are formed in spiral shapes, respectively. Further, accordingto the example of FIG. 9(a), the center of the spiral is within thecrystal growth surface and according to the example of FIG. 9(b), thecenter of the spiral is outside of the crystal growth surface.

The void means a space which is not filled with the materials of thesupporting substrate and base crystal layer or the reaction product.

The area of the void (area in the cross section perpendicular to themain face of the supporting body) may preferably be 1 μm² to 0.8 mm².Further, the height of the void (dimension in the direction of thenormal line P perpendicular to the main face) may preferably be 1000 nmor smaller and more preferably be 500 nm or smaller. Although the lowerlimit of the height is not particularly defined, it may be 1 nm orlarger.

Further, the ratio of the area of the void of the base crystal layerwith respect to the whole crystal growth surface may preferably be 5 to80% from the viewpoint of the present invention and more preferably be15 to 60% on the viewpoint of the productivity.

The presence and height of the void is measured by observing the crosssection by an electron microscope. The conditions are as follows.

Measuring System:

Electron microscope (“SU8240” supplied by HITACHI High Technologies Co.Ltd.) is used to perform the observation of the microstructure.

Measurement Conditions:

A sample is produced by a FIB (focused ion beam) method to form thecross section, which is observed at an acceleration voltage of 3 kV.

The planar (two-dimensional) shape and area of the void is visualized byirradiating light from the bottom surface of the sample and by observinga transmittance image by a differential interference microscope.

According to a preferred embodiment, provided that the raised part 5 isviewed along the cross section perpendicular to the main face 1 a of thesupporting substrate 1 (refer to FIG. 1(b)), the angle θ of the specificcrystal axis a of the crystal of the group 13 nitride with respect tothe normal line P of the main face is smoothly changed. It is thuspossible to further reduce the dislocation density of the layer of thecrystal of the group 13 nitride formed thereon efficiently. The specificcrystal axis may be the c-axis, m-axis or a-axis and more preferably bethe c-axis.

For example, as shown in FIG. 2(a), when the thin film of the layer 7 ofthe crystal of the group 13 nitride is formed on the base crystal layer,the dislocation density can be reduced. Further, as shown in FIG. 2(b),when the thin film of the layer 8 of the crystal of the group 13 nitrideis formed on the base crystal layer as shown in FIG. 2(b), in additionto the reduction of the dislocation density of the layer of the crystalof the group 13 nitride, cracks can be suppressed and the warping of thelayer of the crystal of the group 13 nitride can be also suppressed.

The wavelength of the laser light is made a wavelength whose energy ishigher than a bandgap of the group 13 nitride forming the seed crystallayer to be processed and lower than a bandgap of the material of thesupporting substrate. By this, at the time of irradiating the laserlight from the side of the supporting substrate, the laser light passesthrough the supporting substrate and then is absorbed by the group 13nitride forming the seed crystal layer to heat it to perform theprocessing.

The conversion of energy (unit: e V) and wavelength (unit: nm) can becalculated according to the approximate expressionλ≈1240/Eprovided that E is assigned to the energy and X is assigned to thewavelength.

For example, when the supporting substrate is made of aluminum oxide(for example, sapphire or crystalline orientated aluminum) and thenitride of the group 13 nitride forming the seed crystal layer isgallium nitride, as the bandgaps are about 3.4 eV and 8.6 eV,respectively, it is necessary that the wavelength of the laser light isselected in a range of 144 nm and 364 nm.

The source of the laser light includes third, fourth and fifth harmonicwaves of a Nd YAG laser, F2 excimer laser, ArF excimer laser, KrFexcimer laser, XeCl excimer laser, XeF excimer laser, third and fourthharmonic waves of a YVO₄ laser, and third and fourth harmonic waves of aYLF laser. A particularly preferred laser light source includes thethird harmonic wave of a Nd YAG laser, fourth harmonic wave of a Nd:YAGlaser, third and fourth harmonic waves of a YVO₄ laser and a KrF excimerlaser.

The shape of the irradiated laser light beam may be a circle, ellipse,rectangle or line.

The laser profile may be shaped through a beam profiler. The laserprofile may be gaussian, gaussian-like, donut, or silk hat. The beamprofiles of gaussian and silk hat are preferred.

The laser light may be irradiated onto the substrate after it is passesthrough a lens, slit or aperture, for adjusting the irradiation size andenergy density.

According to a preferred embodiment, a pulse laser may preferably beused to adjust the formation of the raised part. Although the pulsewidth of the laser light is not particularly limited, laser light havingthe pulse width of 100 fs to 200 ns may be used. A shorter pulse ispreferable, since the shorter pulse laser light results in a shortertime period of heating the interface GaN, so that the heating andexpansion of nitrogen generated from GaN decomposed by the irradiationof the laser light is reduced. From the viewpoint of controllability ofthe size of the raised part, the pulse width of the laser light maypreferably be 200 ns or shorter and more preferably be ins or shorter.

The energy density of the laser light beam may preferably be 200 to 350mJ/cm² and more preferably be 250 to 300 mJ/cm². As the energy densityis too low, the crystal of the group 13 nitride at the interface isnon-reactive and, as the energy density is too high, the GaN at theinterface is decomposed into the group 13 element and nitrogen so thatthe generation of the appropriate raised part tends to be suppressed.

The irradiation of the pulse laser light may be performed so that pulsesdo not overlap with each other and, preferably, the laser scanning speedand repetition frequency are controlled so that the laser spots overlapwith each other. The laser light beams, each having a weak energy, maybe irradiated and overlapped so that the rapid evaporation of nitrogendue to the decomposition of the crystal of the group 13 nitride can besuppressed to make abnormal parts of the crystal of the group 13 nitridesmaller.

The processing may be performed so that the focal point of the laserlight is positioned at the interface of the base crystal layer andsupporting substrate, or the laser light may be defocused andirradiated.

A diffuser may be placed on a bottom face of the supporting substrateand the laser light may be irradiated through the diffuser. The materialof the diffuser is selected from materials through which the appliedlaser light transmits. An example of the diffuser includes a sapphiresubstrate whose surface is roughened only and a translucent ceramicplate. A diffuser having a surface on which regular or irregularunevenness is formed is further applicable.

The laser light may be irradiated onto the supporting substrate while itis heated. As the heating of the supporting substrate reduces thewarping, it is possible to perform uniform processing over the plane ofthe substrate.

It is possible to suppress abnormal parts generated during theirradiation of the laser light from the side of the supporting substrateby forming a surface protective layer, such as a photo resist, metaldeposition film or the like, on the base crystal layer.

The base crystal layer may be provided by bonding it with the supportingsubstrate. The method of bonding includes direct bonding or bonding byan adhesive agent. Further, in this case, the material of the supportingsubstrate may be silicon. In this case, it is possible to suppressabnormal parts generated during the irradiation of the laser light fromthe side of the supporting substrate.

The laser light may be scanned by patterning or over the whole surfaceof the supporting substrate and it is possible to obtain the effect ofreducing the dislocation density over the whole of the substrate.

The planar pattern of the patterned raised parts may preferably beuniform over the whole plane in a plan view and the same kind of patternmay preferably be repeated regularly. Specifically, the pattern may bemesh-shaped, stripe-shaped, dot-shaped, spiral-shaped or the like (referto FIGS. 7 to 9).

The voids are also formed at the interface due to the decomposition ofthe group 13 nitride caused by the laser irradiation. The voids in thismode are formed mainly inside of the base crystal layer than at theinterface. However, when the voids are formed, the raised parts are notnecessarily formed. The raised parts are not formed without theapplication of a stress sufficiently high for deforming the base crystallayer.

Then, the crystal of the group 13 nitride is grown on the base crystallayer. In this case, although it is preferred to grow the crystal of thegroup 13 nitride by a flux method, it may be an ammonothermal method,HVPE method, MOCVD method or MBE method. In the group 13 nitride, thegroup 13 element is a group 13 element defined by the Period Tabledefined by IUPAC. Further, the group 13 nitride may specifically andpreferably be GaN, AlN, InN or the mixed crystals thereof.

From the viewpoint of making the crystal of the group 13 nitrideself-standing after it is separated from the supporting substrate, thethickness of the crystal of the group 13 nitride may preferably be 300μm or larger and, more preferably, be 500 μm or larger. Further,particularly for spontaneously separating the crystal of the group 13nitride, the thickness may preferably be 1000 μm or larger.

The crystal of the group 13 nitride is preferably a single crystal. Thedefinition of the single crystal will be described below. Although itincludes a single crystal in conformity with the text-book definition inwhich, atoms are regularly arranged over the whole of the crystal, it isnot necessarily limited to this definition and the single crystalincludes a single crystal generally supplied in the industry. That is,the crystal may contain some degree of defects, incorporate deformationand contain impurities, and these crystals are referred to and utilizedas a single crystal distinguishable from a polycrystal (ceramic) andincorporated herein.

When the crystal of the group 13 nitride is grown by a flux method, thekind of flux is not particularly limited, as long as the group 13nitride can be generated. According to a preferred embodiment, a fluxcontaining at least one of an alkali metal and alkali earth metal isused, and the flux containing sodium metal is particularly preferred.

A raw material of a metal is mixed with the flux and used. As the rawmaterial of the metal, a simple metal, an alloy or a metal compound maybe used, and a simple metal is preferred from the viewpoint of handling.

The growth temperature and holding time of the growth of the crystal ofthe group 13 nitride by the flux method are not particularly limited andappropriately changed depending on the composition of the flux.According to an example, when a sodium- or lithium-containing flux isused to grow the group 13 nitride, the growth temperature may preferablybe 800 to 950° C. and more preferably be 850 to 900° C.

According to the flux method, the crystal of the group 13 nitride isgrown under an atmosphere containing gases including a nitrogen atom.Although the gas may preferably be nitrogen gas, it may be ammonia.Although the pressure of the atmosphere is not particularly limited, thepressure may preferably be 10 atm or higher and more preferably be 30atm or higher from the viewpoint of preventing the evaporation of theflux. However, if the pressure is too high, the system becomes bulky, sothat the total pressure of the atmosphere may preferably be 2000 atm orlower and more preferably be 500 atm or lower. Although a gas other thanthe gas containing a nitrogen atom in the atmosphere is not limited, aninert gas is preferred, and argon, helium and neon are particularlypreferred.

According to a preferred embodiment, the crystal of the group 13 nitrideis separated from the supporting substrate. According to the presentinvention, the ratio of the area of the raised part in the supportingsubstrate surface is controlled so that the grown crystal of the group13 nitride can be peeled by spontaneously separation or other methods.The spontaneous separation method is advantageous since the number ofsteps can be reduced. On the other hand, when the crystal of the group13 nitride is separated by processing without the spontaneousseparation, it is possible to control the conditions for the separationartificially, so that the yield can be further improved and thereduction of the yield is low even when the size of the substrate ismade larger.

Laser lift-off (LLO) and grinding are preferred for separating thecrystal of the group 13 nitride from the supporting substrate byprocessing. When the crystal of the group 13 nitride is generated fromthe supporting substrate by the processing, the yield is improvedcompared with the case that the interfacial reaction product layer,metal of the group 13 element or void is not present. The reason isbecause as the thickness of the supporting substrate is made smaller,for example, by the grinding, the supporting substrate is spontaneouslyseparated from the starting point inside of the interfacial reactionproduct layer, metal of the group 13 nitride or void. Contrary to this,when the interfacial reaction product layer, metal of the group 13element or void is not present, as the thickness of the supportingsubstrate is thinned by the grinding, a large stress is applied on thecrystal of the group 13 nitride so that the generation of cracks in thecrystal is facilitated.

A functional device structure is formed on the thus obtained crystal ofthe group 13 nitride. The functional device structure may be used for awhite LED of a high luminance and high rendering index, a blue-violetlaser disk for a high speed and high-density optical memory, a powerdevice for an inverter for a hybrid automobile, or the like.

EXAMPLES Inventive Example A1

According to the Inventive Example A1, a structure (1) shown in FIG.2(a) (refer to Table 1) was obtained according to the method shown inFIG. 1.

Specifically, a monocrystalline sapphire c-plane substrate 1 having adiameter of 4 inches and thickness of 1.3 mm was contained in a MOCVD(organic metal vapor phase deposition) equipment and heated in hydrogenatmosphere at 1150° C. for 10 minutes to perform the cleaning of thesurface. The temperature of the substrate was then lowered to 500° C.and TMG (trimethyl gallium) and ammonia were used as raw materials togrow a gallium nitride layer in a thickness of 20 nm to form the basecrystal layer. The temperature of the substrate was raised to 1100° C.and TMG and ammonia were used as raw materials to grow the base crystallayer 2 composed of gallium nitride in a thickness of 5 μm.

Laser light was then irradiated from the side of the bottom surface 1 bof the supporting substrate 1 to form the raised parts. The bottomsurface 1 b was subjected to finishing by grinding so that the surfaceroughness Ra was made 0.1 to 0.3 μm.

A pulse laser applying a third harmonic wave (having a wavelength of 355nm) of YVO₄ laser was used as a laser light source. The output power was10 W, the repetition frequency was 100 kHz, the pulse width was 20 nsand the light was condensed by a lens having a focal distance of 200 mm.The working distance (a distance between the lens and sample) was 150mm. A galvano scanner was used to raster-scan the laser light while theshot pitch and line spacing of the laser irradiation were changed toobtain the base crystal layers, each having the void, reaction productand raised part shown in Table 1.

The base substrate was then subjected to cleaning by acetone for 10minutes and to ultrasonic cleaning using isopropyl alcohol for 10minutes, followed by cleaning with flowing pure water for 10 minutes.

The gallium nitride crystal 8 was then grown on each of the base crystallayers by the Na flux method.

The base substrate was then mounted on a bottom part of an aluminacrucible having a cylindrical shape and flat bottom with a diameter of190 mm and a height of 45 mm and the resulting melt composition was thenfilled in the crucible in a glove box. The melt composition had acomposition as follows.

Ga metal: 200 g

Na metal: 200 g

The alumina crucible was then contained and sealed in a container of aheat-resistant metal, which was then mounted on a rotatable table in acrystal growth furnace. The temperature and pressure were raised to 870°C. and 4.0 MPa under a nitrogen atmosphere and the resulting solutionwas agitated by rotation to grow gallium nitride crystal for about 4hours. After the completion of the crystal growth, it was graduallycooled to room temperature over 3 hours and the growth container wasthen taken out of the crystal growth furnace. Ethanol was used to removethe melt composition remaining in the crucible and it was collected asample with the grown gallium nitride crystal. It was proved that agallium nitride crystal 8 was film-formed in a thickness of 80 μm ineach sample.

The sample was then subjected to polishing so that the thickness of theGaN film by a flux method was made 10 μm. Thereafter, the surface wasobserved by a differential interference microscope to prove that pits ordisassociation of the crystal was not observed. Further, the X-rayrocking curve was measured to prove that the half value widths were 120seconds and 150 seconds at reflections at the (0002) plane and (10-12)plane, respectively, indicating that the c-axis was not substantiallydeviated.

The dislocation density, warping and cracking of the gallium nitridecrystal layer were then measured and the results are shown in Table 1.

Comparative Example A1

The structure (1) was obtained according to the same procedure as theInventive Example A1. However, different from the Inventive Example A1,the irradiation of the laser light was not performed and the raised partwas not formed. The dislocation density, warping and cracking of thethus obtained gallium nitride crystal layer were measured and theresults are shown in Table 1.

TABLE 1 Inventive Comparative Unit Example A1 Example A1 Samplestructure ( 1 ) ( 1 ) Lasing Shot pitch μm 20 — conditions Line spacingμm 50 — Base Presence or absence present absent substrate of reactionproduct Presence or absence present absent of void Average height nm 2000 of raised parts Ratio of area % 30 0 of raised parts CharacteristicDislocation cm⁻² 2 × 10⁷ 8 × 10⁷ of Density GaN substrate Warping μm 1035 Crack absent absent

Inventive Example B1

The structure (2) shown in FIG. 2(b) was obtained (refer to Table 2).

Further, the base substrate was produced according to the same procedureas the Inventive Example A1, except that the height and dimension of theraised part and the presence and absence of the void and reactionproduct were changed as shown in Table 2.

The gallium nitride crystal 8 was then grown on each of the base crystallayers by the Na flux method.

The base substrate was then mounted on a bottom part of an aluminacrucible having a cylindrical shape and a flat bottom with a diameter of190 mm and a height of 45 mm, and the melt composition was then filledin the crucible in a glove box. The melt composition had a compositionwas as follows.

Ga metal: 200 g

Na metal: 200 g

After the alumina crucible was contained and sealed in a container of aheat-resistant metal container, the container was then mounted on arotatable table in a crystal growth furnace. The temperature andpressure were raised to 870° C. and 4.0 MPa under a nitrogen atmosphereand the resulting solution was agitated by rotation to grow a galliumnitride crystal for about 50 hours. After the completion of the crystalgrowth, it was gradually cooled to room temperature over 3 hours and thegrowth container was then taken out of the crystal growth furnace.Ethanol was used to remove the melt composition remaining in thecrucible and a sample with the grown gallium nitride crystal wascollected. It was proved that gallium nitride crystal 8 was film-formedin a thickness of 1 mm in each sample.

The gallium nitride crystal was then separated from the supportingsubstrate by the laser lift-off method in each of the examples. Laserlight was then irradiated from the side of the sapphire substrate. Apulse laser applying a third harmonic wave (having a wavelength of 355nm) of Nd: YAG laser was used as a laser light source. The pulse widthwas 10 ns, the light was condensed by a lens having a focal distance of700 mm, the distance between the lens and the substrate surface was 400mm, the optical energy density during the laser lift-off was 500 mJ/cm²,and the whole substrate was scanned so that irradiation dots by thepulse laser were overlapped.

The sample was then subjected to polishing so that the total thicknesswas made 400 μm. Thereafter, the surface was observed by a differentialinterference microscope to prove that pits or disassociation of thecrystal was not observed. Further, the X-ray rocking curve was measuredto prove that the half value widths were 70 seconds and 80 seconds atreflections at the (0002) plane and (10-12) plane, respectively,indicating that the c-axis was not substantially deviated.

The dislocation density, warping and cracking of the thus obtainedgallium nitride layer were measured in each of the examples, and theresults were shown in Table 2.

Comparative Example B1

The structure (2) was obtained according to the same procedure as theInventive Example B1. However, different from the Inventive Example A1,the irradiation of the laser light was not performed and the raised partwas not formed. The dislocation density, warping and cracking of thethus obtained gallium nitride crystal layer were measured and theresults are shown in Table 2.

TABLE 2 Inventive Comparative Unit Example B1 Example B1 Samplestructure ( 2 ) ( 2 ) Lasing Shot pitch μm 20 — conditions Line spacingμm 50 — Base substrate Presence or present Absent absence of reactionproduct Presence or Present absent absence of void Average height nm 2000 of raised parts Ratio of area % 30 0 of raised parts CharacteristicDislocation cm⁻²- 5 × 10⁴ 7 × 10⁶ of Density GaN substrate Warping μm 80120 Crack absent present

Inventive Examples C1 to C4

The structure (2) was obtained according to the same procedure as theInventive Example B1. However, different from the Inventive Example B1,the average height of the raised parts was changed as shown in Table 3.The dislocation density, warping and cracking of the thus obtainedgallium nitride crystal layer were measured and the results are shown inTable 3.

TABLE 3 Inventive Inventive Inventive Inventive Unit Example C1 ExampleC2 Example C3 Example C4 Sample structure (2) (2) (2) (2) Lasing Shotpitch μm 100  50 20  1 conditions Line spacing μm 50 50 50 50 Basesubstrate Presence or Present Present Present Present absence ofreaction product Presence or Absent Absent Present Present absence ofvoid Average height nm  5 50 200  500  of raised parts Ratio of area %30 30 30 30 of raised parts Characteristic Dislocation cm⁻² 6 × 10⁵ 8 ×10⁴ 5 × 10⁴ 4 × 10⁴ of GaN substrate Density Warping μm 120  90 80 40Crack Absent Absent Absent Absent

Inventive Examples D1 to D5

The structure (2) was obtained according to the same procedure as theInventive Example B1. However, different from the Inventive Example B1,the ratios of the areas of the raised parts were changed as shown inTable 4. The dislocation density, warping and crack of the thus obtainedgallium nitride crystal layer were measured and the results are shown inTable 4.

TABLE 4 Inventive Inventive Inventive Inventive Inventive Unit ExampleD1 Example D2 Example D3 Example D4 Example D5 Sample structure (2) (2)(2) (2) (2) Lasing Shot pitch μm  20 20 20 20 20 conditions Line spacingμm 100 50 25 10  5 Base substrate Presence or Present Present PresentPresent Present absence of reaction product Presence or Present PresentPresent Present Present absence of void Average height nm 200 200  200 200  200  of raised parts Ratio of area %  10 30 50 70 85 of raisedparts Characteristic Dislocation cm⁻² 3 × 10⁵ 5 × 10⁴ 3 × 10⁴ 1 × 10⁴ 1× 10⁴ of GaN substrate Density Warping μm 110 80 50 40 40 Crack AbsentAbsent Absent Absent Absent

Inventive Example E1

The structure (3) (refer to Table 5) was obtained according to the sameprocedure as the Inventive Example B1.

However, different from the Inventive Example B1, the gallium nitridelayer was film-formed by HVPE method.

Specifically, the base substrate was contained in an HVPE equipment, andgallium metal (Ga) in a source boat heated at 800° C. was reacted withhydrogen chloride (HCl) gas to generate gallium chloride (GaCl) gas, andthe gallium chloride gas and ammonia (NH₃) as raw materials and hydrogen(H₂) gas as a carrier gas were supplied onto the main surface of theheated seed crystal substrate so that the gallium nitride crystal wasgrown on the substrate. The temperature was raised at 1100° C. and thegallium nitride crystal was grown for 5 hours, resulting in thefilm-formation of the gallium nitride crystal 8 having a thickness of 1mm.

After the growth of the gallium nitride crystal layer, as the layer wassubjected to polishing and the surface was observed by a differentialinterference microscope, pits and disassociation of the crystals werenot observed. Further, the X-ray rocking curve was measured to provethat the half value widths were 80 seconds and 90 seconds at reflectionsat the (0002) plane and (10-12) plane, respectively, indicating that thec-axis was not substantially deviated.

The gallium nitride layer was separated from the supporting substrateaccording to the same procedure as the Inventive Example B1 and thedislocation density, warping and cracking were measured. The results areshown in Table 5.

Comparative Example E1

The structure was obtained according to the same procedure as theInventive Example E1.

However, different from the Inventive Example E1, the irradiation of thelaser light was not performed and the raised part was not formed. Thedislocation density, warping and cracking of the thus obtained galliumnitride crystal layer were measured and the results are shown in Table5.

TABLE 5 Inventive Comparative Unit Example E1 Example E1 Samplestructure ( 3 ) ( 3 ) Lasing Shot pitch μm 20 — conditions Line spacingμm 50 — Base substrate Presence or present absent absence of reactionproduct Presence or present absent absence of void Average height nm 2000 of raised parts Ratio of area % 30 0 of raised parts CharacteristicDislocation cm⁻² 6 × 10⁴ 7 × 10⁶ of GaN Density substrate Warping μm 90120 Crack absent present

Inventive Examples F1 to F3 and Comparative Examples F1 to F3

The structure (2) was obtained according to the same procedure as theInventive Example B1. However, different from the Inventive Example B1,the laser output power was changed so that the energy density of thepulse laser irradiated from the side of the supporting substrate wasmade each value shown in Tables 6 and 7. The shot pitch and line spacingof the laser irradiation were 20 μm and 50 μm, respectively.

The reaction product, void, gallium metal and raised part of the thusobtained base substrate were measured, respectively. Further, thedislocation density, warping and cracking of the thus obtained galliumnitride crystal layer were measured. The results are shown in Tables 6and 7.

TABLE 6 Inventive Inventive Inventive Example Example Example F1 F2 F3Energy density 350 300 250 (mJcm⁻²) Thickness of rection 150 100 50product (nm) Composition Al (mol %) 29 37 42 of reaction Ga (mol %) 4025 10 product O (mol %) 31 38 48 Presence or absence present presentabsent of gallium metal Presence or absence of void present presentabsent Presence or 300 200 100 absence of raised part (height (nm))Dislocation density of 4 × 10⁴ 5 × 10⁴ 7 × 10⁵ gallium nitride substrateWarping (μm) 50 70 80 Crack absent absent Absent

TABLE 7 Comparative Comparative Comparative Example F1 Example F2Example F3 Energy density 120 60 Not (mJcm⁻²) irradiated Thickness ofrection absent absent absent product (nm) Composition Al (mol %) — — —of reaction Ga (mol %) — — — product O (mol %) — — — Presence or absenceof absent absent absent void Presence or absence of absent absent absentraised part (height (nm)) Dislocation density of 5 × 10⁶ 6 × 10⁶ 7 × 10⁶gallium nitride substrate Warping (μm) 690 320 450 Crack absent presentpresent

As can be seen from the above, according to the inventive examples, thewarping of the gallium nitride layer was small and cracks were notobserved. Further, when the reaction product was generated under thebase crystal layer, the dislocation density of the gallium nitride layerwas considerably reduced.

According to the Comparative Examples F1, F2 and F3, as the reactionproduct was not generated, the warping of gallium nitride crystal waslarge and cracks were generated.

The invention claimed is:
 1. A base substrate comprising: a supportingsubstrate; and a base crystal layer provided on a main face of saidsupporting substrate, comprising a crystal of a nitride of a group 13element and having a crystal growth surface, wherein said base crystallayer comprises a raised part; a reaction product of a material of saidsupporting substrate and said crystal of said nitride of said group 13element, a metal of a group 13 element and/or a void is present betweensaid raised part and said supporting substrate; and said crystal growthsurface forms a curved line and a height of said crystal growth surfaceon said curved line with respect to said main face is smoothly changed,provided that said raised part is viewed along a cross sectionperpendicular to said main face of said supporting substrate.
 2. Thebase substrate of claim 1, wherein an angle of a specific crystal axisof said crystal of said nitride of said group 13 element with respect toa normal line to said main face is smoothly changed, provided that saidraised part is viewed along said cross section perpendicular to saidmain face of said supporting substrate.
 3. The base substrate of claim2, wherein said specific crystal axis comprises c-axis.
 4. The basesubstrate of claim 1, wherein said supporting substrate comprisesaluminum oxide, and said reaction product comprises aluminum, a group 13element and oxygen.
 5. The base substrate of claim 1, wherein saidraised part comprises a crack or recess formed therein.
 6. The basesubstrate of claim 1, wherein said reaction product is present betweensaid raised part and said supporting substrate.
 7. The base substrate ofclaim 1, wherein said metal of said group 13 element is present betweensaid raised part and said supporting substrate.
 8. The base substrate ofclaim 1, wherein said void is present between said raised part and saidsupporting substrate.
 9. A functional device comprising: said basesubstrate of claim 1; and a functional layer provided on said basecrystal layer.
 10. A base substrate comprising: a supporting substrate;and a base crystal layer provided on a main face of said supportingsubstrate, comprising a crystal of a nitride of a group 13 element andhaving a crystal growth surface, wherein said base crystal layercomprises a raised part; said crystal growth surface forms a curvedline; and a height of said crystal growth surface on said curved linewith respect to said main face is smoothly changed, provided that saidraised part is viewed along a cross section perpendicular to said mainface of said supporting substrate.
 11. The base substrate of claim 10,wherein an angle of a specific crystal axis of said crystal of saidnitride of said group 13 element with respect to a normal line to saidmain face is smoothly changed, provided that said raised part is viewedalong said cross section perpendicular to said main face of saidsupporting substrate.
 12. The base substrate of claim 11, wherein saidspecific crystal axis comprises c-axis.
 13. The base substrate of claim10, wherein a void is present between said base crystal layer and saidsupporting substrate.
 14. The base substrate of claim 10, wherein areaction product of a material of said supporting substrate and saidcrystal of said nitride of said group 13 element is present between saidbase crystal layer and said supporting substrate.
 15. The base substrateof claim 14, wherein said supporting substrate comprises aluminum oxide,and said reaction product comprises aluminum, a group 13 element andoxygen.
 16. The base substrate of claim 10, wherein a metal of a group13 element is present between said raised part and said supportingsubstrate.
 17. The base substrate of claim 10, wherein said raised partcomprises a crack or recess formed therein.
 18. A functional devicecomprising: said base substrate of claim 10; and a functional layerprovided on said base crystal layer.